Effects of Motor and Cognitive Dual-Task Demands on Ankle Dorsiflexor and Plantarflexor Force Control in Older Adults.

Background: Force steadiness can be impaired under dual-task conditions in older adults. Since this impairment is attributed to their limited attentional resources, we hypothesized that the degree of cortical activity involved in muscle contraction would affect force steadiness under dual-task conditions. To test this hypothesis, based on the premise that dorsiflexion requires more cortical resources than plantarflexion, we compared the effects of additional motor and cognitive task demands on force steadiness between dorsiflexion and plantarflexion contractions in young and older adults.

Method: Eighteen young and eighteen older adults performed a force tracking task by applying either isometric dorsiflexion or plantarflexion force concurrently with and without (control) secondary upper-limb motor or cognitive task.

Results: Force steadiness was impaired by both secondary upper-limb motor and cognitive tasks for the dorsiflexors and plantarflexors in older adults. While force steadiness was impaired similarly by additional task demands regardless of the secondary task type for the dorsiflexors, the impairment effect was larger in the secondary cognitive than motor task for the plantarflexors.

Conclusion: The effects of dual-task demand on force steadiness could depend on the degree of cortical activity involved in muscle contraction in older adults.